Irrigation scheduling strategies for cotton to cope with water scarcity in the Fergana Valley, Central Asia

The Central Asian countries face high water scarcity due to aridity and desertification but excess water is often applied to the main irrigated crops. This over-irrigation contributes to aggravate water scarcity problems. Improved water saving irrigation is therefore required, mainly through appropriate irrigation scheduling. To provide for it, after being previously calibrated and validated for cotton in the Fergana region, the irrigation scheduling simulation model ISAREG was explored to simulate improved irrigation scheduling alternatives. Results show that using the present irrigation scheduling a large part of the applied water, averaging 20%, percolates out of the root zone. Several irrigation strategies were analyzed, including full irrigation and various levels of deficit irrigation. The analysis focused a three-year period when experiments for calibration and validation of the model were carried out, and a longer period of 33 years that provided for an analysis considering the probabilities of the demand for irrigation water. The first concerned a wet period while the second includes a variety of climatic demand conditions that provided for analyzing alternative schedules for average, high and very high climatic demand. Results have shown the importance of the groundwater contribution, mainly when deficit irrigation is applied. Analyzing several deficit irrigation strategies through the respective potential water saving, relative yield losses, water productivity and economic water productivity, it could be concluded that relative mild deficits may be adopted. Contrarily, the adoption of high water deficit that produce high water savings would lead to yield losses that may be economically not acceptable.     

基于滤食鱼类天然产力的安康库区生态负荷量测定

为厘清汉江水体鱼类集约养殖与生态负荷量的关系,测定安康库区滤食性鱼类天然鱼产力,测算Ⅱ类水质限定条件下的安康库区生态负荷量,并与以水体磷含量为标准的计算结果比较。结果表明,设定网箱深度3 m,单位水体生态负荷量为193.44 g/m³,总产量控制为10.47×10⁴ t。库区网养单产为100 kg/m³时,网箱养殖面积控制为1.93‰,网箱生态养殖面积与单位面积产量呈反比。     

春玉米叶片光合生理参数对土壤水分的阈值响应及其生产力分级

试验设正常灌水处理和干旱胁迫处理,讨论春玉米叶片的光合生理参数对土壤水分的阈值响应并进行生产力分级。结果表明:正常灌水处理的叶片光合速率(Pn)、蒸腾速率(Tr)和气孔导度(Gs)呈单峰曲线变化,胞间CO2浓度(Ci)和气孔限制值(Ls)对水分变化具有相反的响应变化。干旱胁迫处理下叶片的Pn、Tr在进行控水后明显下降,灌浆以前Pn下降主要是由气孔限制引起的。随着水分胁迫的加剧,光合结构受损,Pn下降,主要受非气孔因素限制。短期干旱胁迫会适当降低玉米的水分利用效率(WUE),但是下降程度不显著,WUE能达到中等水平。长期严重的水分胁迫后,WUE下降明显,与正常灌水处理相比差异极显著。以光合生理参数为指标对玉米土壤水分有效性及生产力进行分级与评价,确定当36.8%<土壤相对湿度(RWC)<42.7%时为低产低效水;42.7%相似文献   

Comparisons of energy balance and evapotranspiration between flooded and aerobic rice fields in the Philippines

The seasonal and annual variability of sensible heat flux (H), latent heat flux (LE), evapotranspiration (ET), crop coefficient (K_c) and crop water productivity (WP_ET) were investigated under two different rice environments, flooded and aerobic soil conditions, using the eddy covariance (EC) technique during 2008-2009 cropping periods. Since we had only one EC system for monitoring two rice environments, we had to move the system from one location to the other every week. In total, we had to gap-fill an average of 50-60% of the missing weekly data as well as those values rejected by the quality control tests in each rice field in all four cropping seasons. Although the EC method provides a direct measurement of LE, which is the energy used for ET, we needed to correct the values of H and LE to close the energy balance using the Bowen ratio closure method before we used LE to estimate ET. On average, the energy balance closure before correction was 0.72 ± 0.06 and it increased to 0.99 ± 0.01 after correction. The G in both flooded and aerobic fields was very low. Likewise, the energy involved in miscellaneous processes such as photosynthesis, respiration and heat storage in the rice canopy was not taken into consideration.Average for four cropping seasons, flooded rice fields had 19% more LE than aerobic fields whereas aerobic rice fields had 45% more H than flooded fields. This resulted in a lower Bowen ratio in flooded fields (0.14 ± 0.03) than in aerobic fields (0.24 ± 0.01). For our study sites, evapotranspiration was primarily controlled by net radiation. The aerobic rice fields had lower growing season ET rates (3.81 ± 0.21 mm d⁻¹) than the flooded rice fields (4.29 ± 0.23 mm d⁻¹), most probably due to the absence of ponded water and lower leaf area index of aerobic rice. Likewise, the crop coefficient, K_c, of aerobic rice was significantly lower than that of flooded rice. For aerobic rice, K_c values were 0.95 ± 0.01 for the vegetative stage, 1.00 ± 0.01 for the reproductive stage, 0.97 ± 0.04 for the ripening stage and 0.88 ± 0.03 for the fallow period, whereas, for flooded rice, K_c values were 1.04 ± 0.04 for the vegetative stage, 1.11 ± 0.05 for the reproductive stage, 1.04 ± 0.05 for the ripening stage and 0.93 ± 0.06 for the fallow period. The average annual ET was 1301 mm for aerobic rice and 1440 mm for flooded rice. This corresponds to about 11% lower total evapotranspiration in aerobic fields than in flooded fields. However, the crop water productivity (WP_ET) of aerobic rice (0.42 ± 0.03 g grain kg⁻¹ water) was significantly lower than that of flooded rice (1.26 ± 0.26 g grain kg⁻¹ water) because the grain yields of aerobic rice were very low since they were subjected to water stress.The results of this investigation showed significant differences in energy balance and evapotranspiration between flooded and aerobic rice ecosystems. Aerobic rice is one of the promising water-saving technologies being developed to lower the water requirements of the rice crop to address the issues of water scarcity. This information should be taken into consideration in evaluating alternative water-saving technologies for environmentally sustainable rice production systems.     

黑龙江西部旱作玉米水肥生产潜力试验研究

以氮肥、磷肥、补水量为试验因子,以玉米产量为指标,利用MINITAB15统计分析软件进行试验设计和数据分析,通过响应曲面法建立水肥相互作用对玉米产量影响的二次多项数学模型。利用模型的等值线图对影响玉米产量的关键因子及其相互作用进行了探讨,以玉米产量为响应值优化得出玉米生产潜力田间试验值的条件:氮肥为241.1 kg/hm2,磷肥为173.1 kg/hm2,补水量为108.3 m3/hm2,玉米田区生产潜力试验值为12 224 kg/hm2。     

华北典型区冬小麦区域耗水模拟与灌溉制度优化

以经校验Aquacrop模型模拟了不同土壤条件下冬小麦水分与产量响应关系,结合北京大兴区土壤分布及其冬小麦实际种植情况,对模型模拟结果进行区域尺度拓展,以此为基础分析了研究区不同灌溉制度下冬小麦耗水量、产量及水分生产率的变化规律,并推荐了与华北地区水资源实际情况相适宜的冬小麦亏缺灌溉制度。结果表明:应用Aquacrop模型能较好模拟冬小麦生育期内土壤墒情和冠层覆盖度的动态变化过程及其生物量与产量情况,可利用经校验后的模型进行冬小麦水分与产量响应关系研究。灌溉定额在300 mm范围内,随着灌溉量增加,耗水量增大;在灌水次数相同条件下,灌溉日期不同,因蒸腾量变化导致耗水量差异显著。在相同处理下总体上降水多年份产量较高,而不同处理之间随着灌溉量增加产量增大;在灌水次数相同情况下,灌溉关键生育时段选择对冬小麦产量形成及水分生产率提高至关重要。以冬小麦增产提效为原则,在灌1水情况下重点保障拔节-抽穗阶段的需水;灌2水情况下重点保障返青-拔节、抽穗-乳熟阶段需水;灌3水情况下重点保障返青-拔节、拔节-抽穗、抽穗-乳熟阶段需水。针对华北水资源严重短缺实际,建议北京大兴区冬小麦采用灌2水的亏缺灌溉制度,较灌4水情况下的灌溉量与耗水量分别减少140、65 mm,能确保75%产量。可见,在与华北类似的资源性缺水区域,选择适宜亏缺灌溉制度,能大幅降低区域灌溉量与耗水量,在稳定区域冬小麦产量及涵养地下水源方面具有重要的现实意义。     

北流市发展“双高一优”农业经验浅析

广西北流市从１９９０年起,调整和优化农业产业结构,仅用几年时间,就使全市的大农业初步形成“三区、八带、九大基地”与种养加、农工商、农科教、内外贸相结合的多产业配套综合经营发展的“双高一优”农业新格局。从１９９０年到１９９３年全市农村经济总收入由８．３亿元增长到３６．２６亿元,增长了３．４倍。农村经济第一产业与第二、第三产业的比重由７３．２：２６．８调整为５５．２：４４．８;农产品商品率由４９．７％提高到６０．５％。１９９３年粮食年平均公顷产量达到１５１５４．５ｋｇ,成为广西第一个“吨粮县（市）”,人均有粮达到４２０多公斤;农民人均纯收入１２１０．９２元。１９９２年、１９９３年均被评为农村经济实力十强县（市）。     

土壤容许流失量研究的进展与趋势

概述了国内外土壤容许流失量（Ｔ值）研究的历史、目前研究的现状和未来的发展趋势,对Ｔ值研究的主要内容如成土速度、土壤养分流失、泥沙淤积损失、土壤流失与土地生产力的关系、保护沟道侵蚀的重要性等做了讲述。介绍了Ｔ值的数学表达和不同国家的Ｔ值标准,阐述了进行Ｔ值双值性研究的必要性,并对Ｔ值研究中存在的问题进行了分析。     

紫色土退化旱地的肥力恢复与重建

常规耕作的水土流失造成紫色土坡耕地土层浅薄化、土壤养分贫瘠化、土壤干旱化及土壤结构劣化等土壤肥力退化问题。 1 984～ 1 996年长期田间试验结果表明 ,聚土免耕通过垄沟网状结构可保持水土 ,其多年平均径流与土壤侵蚀模数分别为 65 7.7m3hm- 2 和5 30 .0tkm- 2 ,而常规耕作的相应值分别为 1 75 4 .0m3hm- 2 和 31 2 2 .0tkm- 2 ,通过聚土与改土结合 ,聚土免耕活土层厚度平均增加 1 1 .8cm ,聚土免耕耕作技术还通过垄沟强化培肥降低土壤容重 ,增加土壤有机质及N、P、K含量 ,改善土壤理化性状 ,恢复土壤肥力。聚土免耕作物产量比平作高 1 5 %～ 30 %。 1 996～ 1 998年秸秆覆盖实验结果表明 ,秸秆覆盖增加土壤有机质和养分含量 ,改善并维持土壤结构。聚土免耕与秸秆覆盖结合有利于土壤养分活化、土壤结构形成与维护 ,是紫色土退化旱地肥力恢复与重建的关键技术。     

水肥耦合条件下作物产量、水分利用和根系吸氮的试验研究

根据1998～2000年两年在北京市水科所永乐店节水灌溉中心开展的冬小麦、夏玉米水肥耦合的田间试验成果的分析研究表明，氮肥效益的发挥与农田水分状况密切相关，低供水水平时(本研究中为冬小麦仅灌拔节水的节水灌溉处理)，肥料的增产效益十分显著，但氮肥贡献率随施肥量的增加而呈递减的趋势。不同的分析方法都表明，在永乐店节水灌溉中心，冬小麦施尿素400 kg/hm²和200 kg/hm²两个施肥水平的试验处理所获得的水(肥)分生产率最高(在不同农田供水状况下)，由于两者的水分生产率差异不大，为提高施肥效率，建议在生产上考虑选择200 kg/hm²的施肥方案较合理。